The invention relates to a laser-processing unit, in particular a laser-welding unit, having an observation device for observing the working point.
When processing a workpiece using a laser beam, it is necessary for the working point on the workpiece to be arranged correctly in the focus of the laser beam which is focused by a focusing unit. Particularly during manual precision processing of a workpiece using a manual welding laser unit, for example when finishing injection moldings by build-up welding, an observation microscope is used to correctly set the focus and the point of impingement of the laser beam on the workpiece. The correct positioning of the workpiece is carried out with the aid of a height-adjustable x-y bench. In order also to be able to process edges or to reach working points on workpiece surfaces which are oriented perpendicular to the x-y plane, it is also necessary for the propagation direction of the focused laser beam relative to the workpiece, i.e. the angle at which the laser beam impinges on the workpiece, to be adapted to the particular position of the working point, and consequently it may additionally be necessary for the workpiece to be tilted relative to the focusing unit.
Published-German Patent Application DE 38 07 471 A1 discloses an apparatus for guiding a laser beam in which the laser beam can be pivoted about two axes which are perpendicular to one another by means of a pivotable deflecting mirror. When processing workpieces that are not planar, e ability to pivot the laser beam about these two axis, allows one to correctly orient the angle at which the laser beam impinges on the workpiece. In this way, the propagation direction of the laser beam can be oriented in the appropriate working point perpendicular to the surface of the workpiece without having to pivot the entire workpiece. However, the known apparatus does not provide an optical aid for monitoring the correct positioning of the laser beam on the workpiece.
A laser-processing unit having an observation microscope is known, for example, from U.S. Pat. No. 5,449,882. In this laser-processing unit, a stationary observation microscope, which allows the workpiece to be observed in the working area of the laser beam, is arranged behind a dichroic mirror. In the known apparatus, the use of a stationary microscope is sufficient, since this apparatus only allows linear displacement of the laser beam within a relatively small working area, and consequently, the focus of the laser beam does not leave the fixed field of view of the observation microscope. Moreover, the position of the focus of the laser beam can only be seen when the beam-impinges on he workpiece, so that the focal position can only be corrected after processing has commenced.
The invention is based on the object of providing a laser-processing unit, in particular a laser-welding unit, which, while having a compact structure and a relatively large working area which can be covered by the laser beam, allows exact positioning and orientation of the laser beam onto the workpiece even before processing commences.
According to the invention, said object is achieved by a laser-processing unit having the features of patent claim 1.
Since a pivotable focusing unit is provided, tilting or pivoting of the workpiece is no longer required in a wide range of applications. Rather, the laser beam is oriented by pivoting the focusing unit which, on account of the low mass which has to be moved, can be positioned more accurately and with less mechanical difficulty. Moreover, the use of a pivotable focusing unit allows a large deflection angle to be achieved with a small focusing lens or a small focusing mirror.
Since, moreover, a dichroic mirror is arranged in the beam path of the laser beam between the laser beam source and the focusing unit, which mirror is assigned an observation device in such a manner that the optical axis of this device coincides with the axis of the laser beam as it propagates downstream of or behind the dichroic mirror, as seen in the propagation direction of the laser beam, correct and accurate positioning of the workpiece in the working point and orientation of the laser beam are possible. The folding or superimposing of the laser beam path and of the observation device ensure that the focus of the laser beam, i.e. the correct working point, is always in the center of the field of view of the observation device, for example congruent with faded-in cross hairs, even when the orientation of the laser beam is changed. In other words, the center of the field of view inevitably and automatically reproduces the impingement point of the laser beam on the workpiece. The correct position of the workpiece is reached when the selected working point on the workpiece surface has been set centrally and in-focus in the observation device. Therefore, the position of the focus can be set exactly at the desired working point even before processing has commenced, i.e. before the laser beam source is switched on.
The arrangement of the dichroic mirror upstream of the pivotable focusing unit, i.e. in the section of the beam path of the laser beam from the laser beam source to the focusing unit, which is in a spatially fixed position inside the laser-processing unit, allows the pivotable laser beam to be observed using an observation device which is likewise fixed, it being possible for the working area of the laser beam which can be covered by the pivoting movement to be larger than the field of view of the observation device. Since the field of view of the observation device automatically and inevitably follows the pivoting movement of the laser beam, it is possible to operate with relatively high magnifications, depending on the particular application.
Further advantageous configurations of the invention will emerge from the subclaims.